The general background of the invention up until about 1984 was well described in prior art reference U.S. Pat. No. 4,533,146. This patent application incorporates that background section by reference. To that background reference, I now add the prior art reflected in U.S. Pat. Nos. 4,533,146 and 4,706,965, and the additional background which follows.
References U.S. Pat. Nos. 4,533,146 and 4,706,965 sought to define a combination of arrow sub-components that could be assembled in a manner which, when combined, provided additional reinforcements in the area near each end of the arrow shaft, and near the center of the arrow shaft, and which could be configured, by trimming prescribed amounts of material from excessively long point inserts, nock inserts, points, and nocks, so as to achieve proper front-to-back balance in the finished arrow.
It was found to be the case that, in 1984, a single very stiff arrow shaft could indeed be used with virtually all bow types, and draw lengths, and bow draw weights, especially bows suitable for use as hunting bows, by using the compliment of components as defined in U.S. Pat. Nos. 4,533,146 and 4,706,965.
However, it has also proven to be the case that as compound bows continued to evolve after 1985, they often incorporated pulley systems that resulted in very high levels of draw force reduction at full draw. At the time U.S. Pat. Nos. 4,533,146 and 4,706,965 were applied for, the average compound bow incorporated a reduction of draw force at full draw in the 30-50% range. Compound bows having this level of letoff generally called for arrows having about 9 grains of arrow weight for each pound of bow draw weight. By 1994, the average compound bow incorporated a draw force reduction percentage in the 60-90% range. Some compound bows having higher levels of letoff built into their pulley systems were found to require only about 4-5 grains of arrow weight for each pound of bow draw weight, when the bow""s limbs were constructed of lighter-weight laminates or pultruded materials than had been in use prior to 1985.
The requirements for longbows and recurves remain essentially unchanged from those described in U.S. Pat. No. 4,533,146, being about 6.5 grains of arrow weight per pound of bow draw weight for longbows, and 7.5 grains of arrow weight per pound of bow draw weight for recurve bows.
Additionally, a resurgence since 1985 in the use of overdraw accessories which allow a given bow to effectively use arrows that are 4-5xe2x80x3 shorter than usual, also served to increase the relative stiffness of any given size shaft when it was cut off to a shorter length, providing a potential for even further reducing the total arrow weight of the arrows for bows equipped with overdraw arrow rest attachments.
Thus, prior to 1985, the total spread of arrow weight ranges for a given draw weight bow, regardless of whether the bow was of longbow, recurve, or compound bow design, would generally range between 6.5 grains of arrow weight for each pound of bow draw weight (for longbows with no letoff), to 9 grains of arrow weight per pound of bow draw weight (for compound bows with 30% letoff). Thus a 60# draw weight bow of any type could have it""s matching arrow-weight requirements met by producing arrows whose total weight ranged from 390 grains to 540 grains, using the component mix defined by U.S. Pat. Nos. 4,533,146 and 4,706,965, with a variance of 150 grains in overall arrow weight. The variance of 150 grains in this instance represents a 52% increase of the heavier arrow""s weight compared to the lighter arrow""s weight.
By 1990, it had become the case that a compound bow of a given draw weight might require arrows with weight characteristics varying from 4.5 grains of arrow weight per pound of bow draw weight (for a short draw length compound bow having light mass weight limbs and having a reduction in draw force in the 80% range, coupled with use of an overdraw arrow rest attachment and very short arrows), up to 9 or more grains of arrow weight per pound of bow draw weight (for a compound bow having heavy mass weight limbs, and using full length arrows, and having a 25-30% letoff in draw force at full draw). The overall weight requirements for a given compound bow in the 60# draw weight range after 1990, might therefore vary from 270 grains up to 540 grains. The 270 grain variance in overall arrow weights in this instance represents a 100% increase of the heavier arrow""s weight, when compared to the lighter arrow""s weight.
The current greater spread of arrow weight requirements for a given draw weight of bows, of all bow types, effectively requires that between two different compound bows of equal draw weight, because of differences in limb mass and letoff characteristics, one bow might require an overall arrow weight that is two or more times as great as the other bow. Variances of this magnitude cannot be optimally accommodated by the prior art approaches described in U.S. Pat. Nos. 4,533,146 and 4,706,965, especially for hunting bows with relatively light draw weights.
Evolution in compound bows since 1985 has served to effectively negate much of the advantage relating to U.S. Pat. Nos. 4,533,146 and 4,706,965 which called for a single size arrow to be constructed for all different bow draw weights and draw lengths. Since 1985, evolutionary changes in compound bows have introduced an increased need for more than one size arrow to be produced so that every bow, regardless of type, limb mass, draw weight, draw length, and percentage of pulley system reduction in draw force at full draw, can achieve an optimum match of arrow mass (weight) to bow peak weight, and bow letoff.
From a practical standpoint, the changes to compound bows, especially since 1989, relating to increasing the level of draw force reduction at full draw by a significant amount, coupled with a resurgence in the use of overdraw attachments to the bow risers, and use of lighter mass materials in the bow""s limbs, have again introduced such a significant difference between how stiff and heavy a shaft might need to be to be optimally fitted to a given bow, for the broader range of bow draw weight, draw length, limb mass, and draw force reduction (letoff) ranges now possible, that attempting to meet the needs of all bows with a single size shaft column became much more difficult, and increasingly less practical than had been the case earlier.
Given the evolutionary changes in bow configurations (overdraws) and increased letoff percentages built into many current-day compound bows, a single size shaft that would be stiff enough for all draw weights and draw lengths would often be heavier than necessary or desirable, even with the lightest of end-mounted components, when it comes to achieving an optimum arrow (weight) ratio for a given draw weight bow, especially low draw weight bows, having limbs constructed of light mass materials, and having pulley systems with high letoff percentages.
Conversely, an given size arrow that was light enough to be optimal when used from a very light draw weight bow, with a very high percentage of draw force reduction at full draw, and with short draw length, with the draw length possibly made even shorter by use of an overdraw, would often either be too limber for heavier draw-weight bows equipped with heavy mass limbs, and having a low letoff percentage, or not weigh enough to properly load the limbs sufficiently to preclude a dry-fire effect in the heavier draw weight bow.
At the time U.S. Pat. Nos. 4,533,146 and 4,706,195 were applied for, the single arrow for all sizes of bows, especially hunting bows, was a sound and practical concept. However, by 1990, continuing evolution in the compound bow area had significantly offset the usefulness of this aspect of these prior art references.
The other aspects of these prior art references remained in tact: those being the desirability of a means of additionally reinforcing the central section and the ends of the arrow shaft, and a means of providing a simple combination of standard size, but adjustable as to weight, components that could be mounted at either end of the shaft to build the proper front to back balance into the finished arrow. The approaches defined in U.S. Pat. Nos. 4,533,146 and 4,760,965 were adopted by several manufacturers of arrow shaft components.
At least one manufacturer continues to utilize a shaft design which incorporates thicker reinforcement cross sections and a larger outside diameter near the center of the shaft, though this manufacturer""s shaft design does not include parallel outside surfaces, instead being somewhat barrel shaped. Several manufacturers now make integral nock/nock inserts, and points, and point inserts that provide trimmable tail sections suitable for varying their weight, and thereby adjusting the front-to-back balance in the completed arrow.
However, given that it is again necessary for arrows to be made in multiple sizes, in order to accommodate all bows in an optimum manner, much of the advantages involved in utilizing a combination of adjustable as to weight components has also been done away with, since each different size of arrow shaft must now have a complete set of adjustable as to weight components prepared for it.
When a single size arrow shaft could be produced to meet all bow requirements, a concurrent system utilizing a single (one size xe2x80x9csetxe2x80x9d) of matching end-mounted components suitable for providing shaft-end reinforcements and adjusting front-to-back balance in the finished arrow, provided greater benefits than is now the case. This approach still works, but because multiple shaft sizes may now be required, this approach does not offer as great a benefit level as was intended at the time the invention was made.
The trimmable components defined in prior art reference U.S. Pat. No. 4,533,146 are somewhat more costly to produce than are fixed-weight components, and require additional labor (trimming) prior to assembly. Absent a corresponding single arrow shaft suitable for all bows, the greatest benefit of the trimmable, adjustable-as-to-weight, components is provided to arrow assemblers, who can produce more than one length and weight of finished arrow while maintaining fewer total components in their inventory. The advantages to the end users of the shafts made with trimmable-as-to-weight end components is negligible, assuming fixed weight components could be used to effect the same front-of-center balance in the finished arrow.
Further developments since 1985, in the evolution of hunting points, has also given rise to an understanding as to how the height of a given broadhead""s blades may affect optimum front-to-back balance in hunting arrows, and how overall arrow velocity also may impact optimum arrow point selections.
While prior art references describe a preferred front to back balance point as being 10% in front of the shafts lengthwise center (for hunting arrows and excluding the point length itself), it is now known that arrows using broadhead arrow points whose blades stand higher than average (during flight to the target), require a somewhat greater percent-front-of-center balance point in the finished arrow, in order to offset the added turbulence and windplaning that accompanies higher standing blade edges. It should therefore be added to the prior art dissertations re: front-to-back balance in arrows used for hunting, that the ten percent front of center balance point may be the minimum percent front of center for hunting arrows, especially arrows outfitted with broadhead points having high standing blades attached to them.
It has also recently been shown that the faster an arrow is propelled from the bow, the lower the edges of hunting points should protrude from the point centerline, in order to effect optimum arrow flight. It should therefore also be added to the prior art dissertation re: front-to-back balance in arrows, that faster flying arrows, especially very light weight arrows, may need balance points more than ten percent front-of-center for optimum flight when hunting points are used.
Finally, it should be added to prior art dissertations relating to front-to-back balance in arrows that shorter, and lighter arrows which are more susceptible to deviation from point of aim due to wind gusts can often profit from a front-of-center balance point greater than ten percent of the shaft""s length.
In summary, recent evolution in bows, especially compound bows having lighter mass limbs which accelerate arrows forward faster, and arrows now often optimally made lighter than prior art deemed desirable, and points, especially hunting points, have served to modify, to a measurable degree, the requirements regarding proper front-to-back balance in arrows, especially arrows equipped with hunting points.
Given the aforementioned evolutionary changes to bows arrows, and points, it can now be stated that, currently, the optimum balance point for a finished hunting arrow will lie at a point between ten and fifteen percent in front of the lengthwise center of the shaft (excluding the point), depending upon the overall length of the shaft, the weight of the shaft column itself, the speed the shaft is propelled forward at, and the height of the blades on the hunting points being used.
It is an object of the present invention to provide an improved arrow shaft.
It is a further object of the invention to provide an arrow shaft, having substantially parallel outside surfaces, which incorporates in an integral manner additional reinforcements at each end of the shaft, and which eliminates the need to produce different weights of end-mounted components such as nock, nock insert, point, and point insert for different lengths of the same size shaft, in order to effect the desired front-to-back balance in the finished arrow, typically currently determined to be in the ten to fifteen percent front-of-center range, though other front-of-center balance point xe2x80x9crangesxe2x80x9d are certainly accomplishable within the scope of the inventive arrow shaft.
It is a further object of the invention to provide an arrow shaft which has improved hoop strength.
In the event future evolution in compound bows and hunting points mandates further modifications to the optimum percent front-of-center balance point for arrow shafts, the general features of this invention including a method for providing, in an integral manner, improved front-to-balance point in arrows; and the method of this invention for providing, in an integral manner, the desired additional reinforcement in the shaft column at each end, and otherwise wherever additional columnar strength and hoop strength are needed, will continue to provide an optimum means of accomplishing both objectives.
According to a broad aspect of the invention, there is provided an arrow shaft having substantially parallel outside surfaces.
The shaft incorporates a core of porous and very lightweight material around which reinforcing materials are wrapped. The core material has a substantially round cross-section at all points along the length of the shaft, but not all sections of the core material have the same outside diameter. At each end of the shaft for a prescribed distance, the core material is reduced in diameter. One or more other sections of the core, intermediate the end sections, may likewise be reduced in diameter from other core sections intermediate the endmost sections of the core.
A combination of reinforcing materials running in the lengthwise direction for warp (lengthwise) strength, both compressive and tensile, and materials running helically around the core, for hoop strength, are wrapped around the core materials in such a manner that the resulting arrow shaft has substantially parallel outside surfaces along it""s entire length. Those areas along the length of the shaft underneath which the core material itself was of reduced diameter incorporate greater thicknesses of reinforcement materials, so as to create an outside surface still having substantially parallel edges.
The reinforcement materials are selected to be heavier, and usually also much stronger, than the core materials. The result is an arrow shaft column that is not only substantially reinforced, from a strength standpoint, at each point along the length of the arrow shaft column that is underlaid by a core section of reduced diameter, but which is also heavier at the same points which are thus additionally reinforced.
It can be easily seen that by strategically selecting the specific areas, and lengths of each, to be additionally reinforced along the length of the shaft, that a composite shaft column can be produced which also achieves a prescribed front-to-back balance in it, such that a given single size and weight of nock insert, nock, point insert, and point, produces in the finished arrow the required front-to-back balance within a specified range, typically at the current point in time determined to be ten to fifteen percent in front of center, for all hunting arrow lengths, of the same given shaft size.
It can further easily be seen that by strategically selecting the positioning and lengths of the additional thicknesses of reinforcing materials along the length of the shaft column, including additionally reinforcing each end section of the shaft column, that the completed arrow can achieve both the desired strengthening at the ends of the shaft, and the desired front-to-back balance, when using a single fixed point weight and fixed point insert weight, for all lengths of the same shaft size, said reinforcements and front-to-back balance being achieved in an integral manner, with the additional reinforcements and front-of-center balance characteristics being integrated directly into the shaft column itself, rather than being achieved through use of either a variety of different fixed-weight assembly components, or a single set of adjustable-as-to-weight nock inserts, nocks, point inserts, and points, for a given shaft size.
The inventive method of providing the desired front-to-back balance point in the inventive arrow shaft by means of adding more weight and strength to the front part of the shaft, than to the back part of the shaft, provides an unexpected additional benefit aside from establishing the desired front-to-back balance point in the finished arrow while using non-adjustable-as-to-weight end components. The added benefit is the improved flight dynamics accomplished by spreading the additional front-of-center weight out over a longer length of the arrow shaft column itself.
Prior art methods of obtaining the desired front-of-center balance point in the overall arrow call for cementing in place a point insert to which a point is attached, or alternatively cementing in place a point in or over the end of the shaft column itself The point insert and point combine to achieve the desired amount of additional weight at the front end of the arrow, and may also provide some additional reinforcement to the front end of the arrow as well. Typically, the point insert, even when a trimmable-as-to-length insert is used, places the entire amount of combined point and point insert weight within an one to three inches of the endmost area of the front-end of the shaft column. Trimmable-as-to-length inserts and points also require a generally tubular shaft column for their mounting.
Prior art methods of producing the desired front-to-back balance, result in a finished arrow that has a considerably heavier combined point and point insert weight positioned at the very front-end of the shaft column, which causes the front-end of the arrow to drop down more rapidly than the back end of the arrow drops, once the apex of the trajectory curve is reached. The heavier the combined weights at the very front-end of the shaft column, when compared to the weights at the other end, and near the center of the shaft, the more rapidly the front-end of the arrow drops, when compared to the back-end of the arrow, after the apex of the trajectory curve is reached.
Conversely, the arrow shaft of this invention distributes more of the additional weight needed at the front of the arrow to effect proper front-to-back balance, along a substantially longer section of the front half of the shaft column itself, and uses a lighter combined weight point and point insert than would be called for with prior art shafts, in order to achieve the desired overall weight in the front half of the arrow.
The inventive shaft therefore provides, as an added benefit, a means of improving the resultant arrow trajectory curve, for a given overall weight of arrow, having a given front-to-back balance percentage, by reducing the tendency of the arrow to nose over, and xe2x80x9cdivexe2x80x9d more rapidly toward the ground, after the peak of the trajectory curve has been reached.
The inventive arrow shaft produces another benefit aside improving the trajectory potential derived from spreading the desired additional front-of-center weight out over a longer length of the shaft column. The providing of additional weight in the front part of the shaft column itself, means that a lighter weight point, and/or point insert is needed to effect the proper overall front-to-back balance in the finished arrow.
The lighter combined point and point insert weights called for when using the arrow shafts of this invention provide a lower total amount of fixed inertia mass, related to front end components mounted at the very front end of the arrow, that has to be overcome during acceleration. The reduced point and point insert weights called for in the inventive arrow shaft, in turn allows somewhat less stiffness to be built into in the central area of the shaft column while still maintaining a shaft column that is suitably stiff so as to avoid excessively buckling when being accelerated out of the bow. The reduced stiffness requirements in the central section of the shaft column, in order to accommodate lighter point weights, while still maintaining optimum front-to-back balance in the overall arrow, will generally allow shafts of a given size to be made somewhat lighter, when constructed of a given compliment of composite materials.
More important however is, that by providing a solution that achieves the sought after benefits relating to front-to-back balance in the overall arrow, the reduced point weights called for when employing the inventive arrow shaft, serves to significantly reduce bending moments imparted to the center section of the shaft during the acceleration period, and thereby serves to improve accuracy and arrow flight stability as well over prior art approaches, while using less reinforcement materials of a given type near the center of the shaft column than would be required with prior art approaches.
The inventive arrow shaft is neither a truly tubular design or a solid design. It incorporates the best features of both of these prior art shaft types. The central core of the shaft, made of very lightweight and porous materials, is used as a mandrel during the lay-up process. The core mandrel is thereafter left in the arrow shaft and not removed. This aspect of the invention serves to greatly simplify the manufacturing process. Prior art approaches to constructing composite arrow shafts have required that polished mandrels be used during the curing cycle. Removal of mandrels is a time consuming process, and therefore adds to the cost to produce tubular composite shafts. Mandrel-based arrow shaft manufacturing operations involving composite construction methods also require that mandrels be frequently xe2x80x9cstrippedxe2x80x9d (cleaned) with a caustic agent, which over time erodes the mandrels and forces mandrel replacement. The manufacturing process for producing the inventive shaft avoids all of these mandrel-related operations and costs.
Because the core incorporates larger outside diameter sections intermediate the ends of the shaft column, the core material is effectively mechanically locked into place, as well as having an adhesive bond between the core materials and the outer reinforcing materials, and the core is thereby made doubly inseparable from the outside reinforcement materials.
The feature of the inventive arrow shaft calling for a core section to be comprised of sections having different diameters at different points along the length of the arrow shaft column, circumvents problems encountered by producers of composite shafts which are comprised of tubes having parallel outside surfaces which serve as a non-porous mandrel during manufacturing operations, overlaid with, and cemented to, fiber reinforcement materials, resulting in the xe2x80x9cbarrel shapedxe2x80x9d shafts alluded to earlier. In these prior art shafts, a breakdown in the bond between the non-porous, parallel-outside-surfaced, mandrel material (typically aluminum) and the overlaying fiber reinforcement materials (typically graphite), sometimes allows the inner xe2x80x9cmandrelxe2x80x9d section to separate from, and slip out of, the outer fiber reinforcement layers during acceleration and/or impact, thereby rendering the arrow useless from that point in time forward.
In a preferred embodiment of the inventive arrow shaft, the diameter of the core material at the ends of the shaft column are selected to be the same as the diameter(s) of the male section(s) of the nock and/or point insert that will be used in the finished arrow. The core material is removed (drilled out) a sufficient distance to allow the nock/nock insert and point/point insert to be fitted into each end of the shaft. The inserts are thus cemented not to the core material, but to the outside reinforcement materials at each end of the shaft. In prior art composite shafts which left the tubular xe2x80x9cmandrelxe2x80x9d in the shaft after adding reinforcement materials, the nock and point inserts were cemented directly to the inside tube surface of the mandrel, rather than to the outside reinforcing materials. Thus, when the adhesive bond between the mandrel and outside reinforcing materials broke down, the point and mandrel were both free to disengage completely from the outer reinforcement materials.
The inventive arrow shaft does not rely totally on the adhesive bond between the core materials and the outer reinforcing materials to keep the core materials in place during acceleration, impact, or at any other time. The mechanical lock provided by the larger outside diameter core sections intermediate the ends of the shaft column precludes movement of the core regardless of the strength of the adhesive bond between the core and outside reinforcing materials.
However, it is also the case that by selecting the core to be made of a porous material, that the adhesive bond between the core of the inventive arrow shaft, and the outside reinforcing materials in the inventive arrow shaft, will be more reliable than the adhesive bonds achieved in prior art composite shafts alluded to earlier, which employed non-porous mandrels overlaid by reinforcements, resulting in a shaft column having a somewhat barrel-shaped outside surface. The cementing of the nock and point inserts directly to the outer reinforcing material layers provides a third locking mechanism for precluding movement of the core materials at any point in time.
Retaining the core material, mechanically locked in place and cemented to the outside reinforcement materials, provides significant stiffening in the overall shaft column. The improved sectional density of the composite column, combines with greater reinforcement stiffness in a manner that produces further additional benefits in terms of enhancing the penetration potential of the arrow, enhancing accuracy, and quieting the downrange flight of the arrow. The added stiffness obtained by retention of the inner core material, coupled with the additionally reinforced front end of the shaft column, aids the shaft column in staying straight at the time of impact, and serves to maximize the amount of kinetic energy in the column that is concentrated in a single direction at the time of impact, thereby enhancing the penetration potential of arrows made using shafts of this invention.
The added stiffness, and the manner in which the core materials are joined to the outer reinforcement materials such that bending moments affecting any point along the shaft""s length are both offset by materials on the opposite side of the shaft column, and by the underlying core materials, serves to dampen any harmonic vibrations imparted to the shaft column during acceleration, and thereby serves to restore stability more quickly, which positively impacts shooting accuracy, and also serves to reduce noise relating to harmonic vibrations in the shaft when such vibrations are present.
The inventive method of shaft construction yields another benefit not present in prior art composite shafts. The retention of the core materials serves to significantly improve the hoop strength of the shaft column at all points along it""s length. Improved hoop strength serves to improve durability in the arrow when it comes in contact with sudden pressure coming against the side of the column, such as when a misdirected arrow inadvertently xe2x80x9cskipsxe2x80x9d off of a log, tree branch, or rock.